1. Technical Field
The present invention relates to direct access storage devices in general, and in particular to magnetic storage devices. Stills more particularly, the present invention relates to a method for indexing magnetic disks by means of a scanning probe.
2. Description of Related Art
Severe performance problems on magnetic storage media may be caused by mechanical/magnetic defects, thickness variations of layering sequence or variations in magnetic coupling in or on top of the magnetic layers in the nanometer range of the magnetic storage media. Hence, certain techniques that enable the mapping of surface and magnetic properties of those critical areas (or areas of interest) with a very high spatial resolution are required. In addition, those techniques should be applicable in-situ in order to detect and characterize the cause of failures. Furthermore, those techniques should be incorporated within a test routine that allows critical areas to be characterized in a relatively short time frame.
One prior art approach for imaging hard disk defects is by characterizing a hard disk on a spin test stand (STS). With such approach, the magnetic and/or topographic properties of a spinning hard disk is analyzed by using test heads such as read write heads that are commonly used in hard disk drives. Some test heads may be specifically designed for test procedures that feature higher resolution, bandwidth, or cover larger tested areas. Defects on a nanometer scale detected by an STS analysis can be mapped by a scanning probe microscope that is attached separately to the STS. For even higher accuracy, the common co-ordinate system given by a rotating spindle on which the storage media are mounted can be used. One requirement for such test technique is that the storage media stationary during both the writing process and the positioning process. Otherwise, the common co-ordinate system between the two measuring schemes will be lost. In other words, any deviation between the center of rotation and the center of the circular data tracks cannot be tolerated. Sometimes, such deviations may even be caused by removing a disk from the spindle and then placing the same disk back on the spindle again. Consequently, data or servo information in the storage media have to be deleted or overwritten by the test mechanism.
However, it is often not very convenient to overwrite additional magnetic information to hard disks because that would change the existing magnetic domains (or magnetic transitions) in the hard disk that might be the cause of performance problems. Another drawback of the above-mentioned overwriting approach is that, in some cases, failures of the magnetic media or magnetic failures can only be detected in a hard disk drive after a servo pattern has been written. Therefore, a nanometer level precision analysis of magnetic media as they come from the hard disk drive are very desirable. A mechanism or tool that is capable of using the existing magnetic transitions, such as the tracks of servo pattern, for exact positioning of the scanning probe is also very desirable.
Another prior art approach relies on magnetic marking techniques and detection of marked areas under an optical microscope. A typical magnetic marking technique is by using a ferrofluidic liquid that is brought on top of the magnetic media. Disadvantages of such approach include additional optical devices and many different analyzing steps are required and time consuming. In addition, not all defects can be found under an optical microscope, especially when no marking techniques are available. Furthermore, ferrofluidic liquid is often destructive to magnetic storage media.
Consequently, it would be desirable to provide an improved method for indexing magnetic storage media.
In accordance with a preferred embodiment of the present invention, a magnetic disk includes several essentially concentric magnetic tracks. The magnetic disk is attached to a rotating spindle. A number of data tracks is then written in a specific circular arc at an inner radial position of the magnetic disk. The beginning or the end of the written data tracks is defined to be in a co-incident or in a defined relation to an index or trigger signal defined by the rotating spindle. The rotating spindle is stopped from rotation, and a scanning probe microscope is moved radially at a fixed rotating angle to a second radial position. A tip of the scanning probe microscope is moved towards a surface of the magnetic disk. At least one scan line is recorded and analyzed in order to determine if a magnetic track is imaged by the tip of the scanning probe microscope.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.